This invention relates to pipeline couplings and has particular, though not exclusive, application to the coupling of lengths of pipe to form pipelines for conveying fluids at high pressure in oil exploration, oil production and related industries.
Such pipelines commonly comprise a series of interconnected lengths of steel pipe, adjacent lengths of which may be interconnected with one another by any one of a number of different coupling arrangements dependent upon the location and application of the pipeline in question.
One known coupling arrangement comprises a flat annular plate welded or screwed to each end of each length of pipe, said lengths being interconnected by means of a series of angularly-spaced nuts and bolts passing through abutting plates on the adjacent ends of the lengths to be connected, a gasket or ring type seal being located between the abutting plates.
Coupling arrangements of this type, which it will be appreciated are somewhat time-consuming to effect and dismantle, are commonly used on installations of a permanent nature where the time involved in installing or replacing the coupling is not of importance.
A further known coupling arrangement comprises a clamp surrounding the adjacent ends of two lengths of pipe to be interconnected, said ends having tapering external flange portions formed therearound, and the internal surface of the clamp having corresponding internal tapered regions formed thereon for co-operation with said flange portions on the pipe lengths. On tightening of the clamp, which may consist of two or more components, around the ends of the pipe lengths by means of associated nuts and bolts, said lengths are drawn axially towards one another to compress a seal located therebetween and to effect the joint.
Clamp couplings of this general type are more compact than the above-detailed flange couplings and are therefore used in locations where space is at a premium and where the weight of the coupling is to be taken into account. However, again, clamp couplings of this type take time to install and replace and are therefore only appropriate in permanent or semi-permanent installations.
It is sometimes necessary for pipeline couplings to be quickly and easily released or effected and, in such a situation, it is common practice to use a union incorporating an internally-threaded nut on one component co-operating with an external thread on the other component.
A preferred coupling of this nature is the so-called hammer lug union. Such a union comprises a male connecting piece at one end of a length of pipe and carrying thereon an internally-threaded nut the outer wall of which is provided with a series of radially-projecting, circumferentially-spaced lugs, and a female connecting piece at the other end of the length of pipe, said female connecting piece being externally threaded and housing therein an annular sealing ring.
Interconnection of two lengths of pipe is effected by locating the end of the male connecting piece of one length into the female connecting piece of the other length, drawing the nut over the male connecting piece and onto the correspondingly-threaded portion of the female connecting piece and tightening the nut onto ..said female connecting piece by hammering tangentially on the lugs of the nut. Sealing is achieved by co-operation between the abutting ends of the two connecting pieces and the seal, over-compression of the seal being prevented by metallic interference of the two connecting pieces.
It will be appreciated that such an arrangement enables extremely quick making and breaking of the connection, such hammer lug unions therefore being used in temporary or semipermanent installations where speed of connection or disconnection is of essence. However, their reliability is not such that they can be used in permanent installations.